Case Studies in Construction Materials (Jul 2023)
Experimental study on the bond performance of deformed steel bar in ultrahigh performance concrete
Abstract
Ultrahigh performance concrete (UHPC) has emerged as a relatively new material showing excellent ductility compared to normal concrete, and it has the potential to be used in combination with steel bars in several engineering application scenarios. The interfacial bond performance is the key to determining the effectiveness of force transfer between different materials, which is required to achieve a refined analysis of member behaviour. In this study, central unidirectional pull-out tests of 54 prismatic specimens with deformed steel bars embedded in UHPC were carried out without lateral constraints. The sizes of the specimens included two types: design size and standard size (200 mm × 200 mm × 200 mm). The design size was related to different combinations between anchorage lengths (2, 3, and 4 times the diameter) and concrete covers (2, 3, and 4 times the diameter) of steel bars, which were also the primary variables of this test. Eighteen standard specimens were used to explore the strain change law along the anchorage length of the steel bar. The specimen was loaded according to the displacement control of 1 mm/min on the static tensile loading system, and a linear variable displacement transducer (LVDT) was arranged on both sides of the loading end and the free end of the specimen to collect data continuously. The strain distribution, anchorage lengths, concrete covers, critical anchorage length, maximum bond stress and bond stressslip model of deformed steel bars in UHPC were all thoroughly investigated. Generally, the results revealed that when the anchorage length exceeded two times the diameter of the steel bar, the maximum strain appeared at approximately 1.5 times the diameter away from the loading end. The maximum bond stress decreased with increasing anchorage length, and the maximum reduction was approximately 54.42%, but this law did not apply to the concrete cover. The maximum bond stress increased with increasing concrete cover, and the gain in peak load was approximately 18.23%. However, the excessive concrete cover did not bring a noticeable gain effect. In addition, compared with several existing bond stressslip models, the improved model proposed in this study was in good agreement with the experimental results, and the determination coefficient of related parameters was basically above 0.95.
